This invention relates to apparatus for purifying fluids. More particularly, this invention relates to apparatus for removing dissolved and undissolved impurities from liquids such as water and the like, where such dissolved and undissolved impurities may be radioactive as occurs with respect to fluids such as water used in nuclear power plants.
Basically, the problems encountered in the purification of fluids such as water are exemplary of those present in the art of fluid purification. Fluids to be purified will generally contain two types of impurities, dissolved impurities and undissolved impurities.
One of the principal methods employed to remove undissolved solids from water, or other fluids, is to pass the fluid through a mechanical filter means, such as a filter screen, filter cloth, filter leaf or the like. With respect to the removal of dissolved impurities from water or other fluids, the use of ion exchange resins has become well known in the art. Such resins, which may be bead type or powdered type as is known in the art, when contacted by a fluid, release ions to the fluid while simultaneously capturing other free ions in the fluid. Accordingly, when a fluid is passed through a bed or beds of these ion exchange resins, the ions of the dissolved impurities are captured by the ion exchange resin particles and replaced by desirable ions released by the ion exchange particles to the fluid. Therefore, the undesirable ions in the water are exchanged for desirable ions given off by the resin particles.
In a typical process for removing dissolved impurities from water, commonly referred to as a demineralization process, the untreated water containing the dissolved impurities, such as salts or electrolytes, is passed through a bed of cation ion exchange resin. As a result of the ion exchange between the cation ion exchange resin and the water, the salts are changed to corresponding acids. Thereafter, the water is passed through a bed of anion ion exchange resin wherein an ion exchange reaction removes the acids. As a result, there occurs a significant removal of dissolved impurities.
As will be recognized by those skilled in the arts, however, particular and unique problems are presented when the fluid contaminants are radioactive.
The removal of dissolved and undissolved solids from fluids when such dissolved and undissolved solids are radioactive inevitably results in a build-up of radioactive material within the purification apparatus. Passage of undissolved solids through mechanical filter devices causes a build-up of the undissolved solids on the filter structure with the resultant concentration of radioactivity at the filter. Similarly, the removal of dissolved solids by passage through a demineralizer bed of ion exchange resins also results in a build-up of radioactive materials within the demineralizer bed.
This problem of radioactive build-up has been recognized in the art. Accordingly, it is the present practice to permit concentration of radioactive materials to exist up to acceptable limits in a filter apparatus and thereafter to remove the radioactive filter structure as well as any radioactive demineralization resins for transport to a disposal tank. Thereafter, the disposal tank is transported to a burial site and the materials are buried in accordance with accepted regulated procedures. Thus, the radioactive used filters and used ion exchange resins must be handled by personnel and transported from the filter apparatus to a disposal apparatus for burial. Such necessity for handling limits the permissable degrees of radioactive build-up in the filter elements to be disposed of and in the demineralization materials to acceptable radioactive concentration levels. As will be recognized by those skilled in these arts, the upper limit of such levels is approximately 100 Ci.
A disadvantage attendant to the radiation concentration level limitation is that such radiation level occurs prior to the complete usage of the filter apparatus as well as the ion exchange materials. More particularly, it is typically the case that the upper limit of radiation concentration in the demineralize material occurs when the activity of the ion exchange material has been utilized to only approximately 30% of its full ion exchange capability. Similar lack of efficiency has been experienced with respect to mechanical filter elements in the filtration of undissolved radioactive contaminants.
It is clear, therefore, that the filtration and demineralization apparatus and material are not being utilized to their full efficiency thus causing water purification in this manner, where the impurities are radioactive, to be extremely expensive. Furthermore, it will be recognized by those skilled in the art that the handling of radioactive materials by personnel is always a delicate operation and therefore very costly.
A typical example of a situation wherein radioactive impurities are found in water is the miscellaneous drain water occurring in nuclear power electrical generating facilities. In such plants there is a continuous outflow of water from the process equipment. Pumps leak, water is removed for testing purposes, often times equipment such as condensers and pipes may experience leaks.
The normal outflow of waters such as pump leakage, sample waters and the like, must be accommodated on a continuing basis. In nuclear power facilities such impurities are radioactive. Similarly, the abnormal occurrence of waste waters e.g. from condenser leakage, pipe leakage and the like, also presents a radioactive contaminant problem and should be provided for in order to avoid the necessity for plant shut-down other than during ordinary maintenance periods. Such shut-downs, as will be recognized by those skilled in the art, are extremely expensive costing hundreds of thousands of dollars a day.
Known methods and apparatus for purifying such radioactive waste waters involve collection of the waters from around the facility through appropriate drainage into a sump. Thereafter the sump water is pumped into a filtration and/or demineralization apparatus which removes the dissolved and undissolved impurities in order that the water so purified may be returned to the system for reuse or discharged appropriately outside the plant facility.
Such filtration and purification equipment is the type which requires removal of the active demineralization materials and the filter apparatus upon the occurrence of the upper limiting levels of radiation concentration. Thus the known methods and apparatus are both costly by reason of their inefficient use of the purification means as well as limited in the amount of radio-active impurities which may be removed prior to the requirement for shutdown. As discussed briefly above, such shut-down may result in the shut-down of the entire facility.